One of the main tasks for biological research today is to decipher a whole system of biologically relevant information that exists on the cell surface. The regulation of the number and distribution of membrane components is one way in which this information is expressed. Two cell surface molecules whose number and distribution are highly regulated both in vivo and in vitro are the acetylcholine receptor (ACHR) and the acetylcholinesterase (ACHE). These molecules are particularly interesting to focus on because: (a) they have been extensively studied and good tools have already been developed for their study (such as alpha-bungarotoxin), and (b) they are essential components of the neuromuscular junction and their study promises a greater understanding of both the cell surface and cholinergic synapses. We will continue to investigate various aspects of the regulation of ACHR and ACHE molecules on skeletal myotubes in cell culture. Cell fractionation methods as well as pharmacologic and immunologic tools will be used to clearly define the intracellular transport pathways of the ACHE and ACHR. Membrane vesicles containing ACHE and ACHR will be studied by membrane protein crosslinking agents, antibody affinity chromatography and electron microscopy. Development of the ACHE molecular forms will be studied by cell free translation of mRNA. The assembly of the A12 asymmetric form of ACHE will be probed by pharmacologic perturbations of the extracellular matrix.